This invention relates to improvements in weighing systems and in one particular form a cordless electronic weighing system.
Most industrial and commercial electronic weighing systems make use of one or more load cells connected to an indicator or scale. A commonly used term is loadbar, which refers to that part of the weighing system, which receives at least part of the load that is to be weighed (e.g. by means of force, displacement or other measurable quantity) and which contains the transducer, or load cell, to convert that quantity into an electrical signal. A loadbar may contain one or several load cells. Typically 2 loadbars are placed under a platform to make a complete load receptor. A platform with load cells mounted under it should be considered equivalent to (typically) a pair of loadbars for the purpose of this patent.
Sometimes the load cell(s) is/are included inside the indicator, but in many applications the load cells are located in loadbars that are physically separate from the indicator. The loadbars are then connected to the indicator using electrical cables. Typically, these cables provide electrical power to the transducer (and optional other electronic circuits) inside the loadbars, and transfer the signal produced by the transducer (or optional electronic circuits) to the indicator of the weighing system.
In many industrial and agricultural applications for weighing scales the cables connecting the loadbars to the indicator have to be protected to avoid being damaged. Alternatively, mechanically robust cables can be used to withstand a certain amount of rough handling or abuse. When a loadbar cable is damaged the system is temporarily out of action until the cable (which is often part of the loadbar assembly and cannot be separated) is repaired or the assembly is replaced. This can be inconvenient, time consuming and expensive.
The amount of damage to a loadbar cable to make a system unusable is often quite small. It does not necessarily mean that one or more conductors in the cable are severed or shorted. Even just a small break in the insulation jacket of the cable can have a sufficient effect on the accuracy of a weighing system. The reason for this is that the load cells in many loadbars are based on the use of resistive strain-gauges, which produce relatively small signals (in the order of a few millivolts or less, full scale) and have a relatively high source impedance (typically in the order of a few hundred ohms). In such a system based on resistive strain gauges, if a break in the loadbar cable insulation jacket allows a small amount of moisture to enter the cable and make some electrical contact between wires inside the cable, or to work its way down the cable and into the load cell, accuracy is often affected to the point where cable repairs are necessary to restore weighing system performance to an acceptable level.
Weighing systems employing loadbars and a remotely located indicator are often used in unfriendly environments. One example is animal farming which is very inhospitable for electronic devices due to, amongst other things water, dung, urine and sharp hooves.
Therefore, in such an environment, and taking into account the strong possibility of cable damage, the occurrence of damage creates significant problems for the farmer. For example, damage is usually noticed when the farmer intends to start weighing. Consequently stock will usually be in the yards and a stock truck may be present. Thus there is considerable user inconvenience, not to mention frustration and expense, to cancel a day or a weeks work to get the scales repaired.
Diagnosis of cable damage faults can be difficult for the farmer. For this reason a fault may not be noticed until after erroneous weighing results have occurred. This can be another source of expense to the farmer as the farmer is often effectively paid by weight.
A further source of expense to the farmer is the cost of repair. A cable must be repaired professionally to prevent future moisture ingress. Moisture that has entered through the cable damage can travel inside along the cable and get into load cells.
Thus in set-up the farmer needs to ideally route the cables where they will not get damaged easily. This is often not possible or easy to achieve. Also positioning of the indicator is relevant and may have some bearing on cable routing.
The present invention is not limited to weighing equipment based on the use of resistive strain gauges. The invention is applicable to other types of systems, which normally employ electrical wires between the loadbars (or, more generally speaking, the transducers therein) and the indicator.